This invention relates to a display data processing device for reading code information displayed on a certain display area of TV screen by interlace scanning (NTSC system television), and outputting the information to a printer or display unit.
There have been recently developed devices for reading coded information such as characters and pictures displayed on part of a TV screen by means of a photo sensor, and reproducing and delivering the information in the form of characters or pictures by means of a printer or display unit. In such devices, the format of a code 1 displayed in a certain display area of a TV screen is expressed, for example, in 10 bars as shown in FIG. 1, each bar corresponding to one bit, and depending on whether the bars are displayed or not, a 10-bit coded information signal can be displayed.
The code 1 is surrounded by a blank display region 2 and a white frame display region 3, so that only the code 1 can be read by the sensor. In this method, however, because of the presence of blank display region 2 and white frame display region 3, the region actually available for the display of code information is small, and much coded information cannot be displayed at once. To solve this problem, the code may be displayed in the entire code display region as shown in FIG. 2. In this method, a 16-bit coded information signal may be displayed, as compared with the 10 bits of FIG. 1, in the same display area. This method, however, has the problem that the coded information in such format cannot be read correctly when the coded information is displayed in the interlacing scanning method.
That is, in the NTSC system, the scanning lines of the screen are first scanned every other line, in the odd-numbered lines, and the remaining even-numbered lines are scanned the second time, thereby making a complete picture. The number of scanning lines is 525, and by scanning the same screen twice at a vertical scanning time of 1/60 sec, 30 screens are displayed in a second. In FIG. 3 and FIG. 4, thick-lines a indicate a first scanning screen, and thin-lines b denote a second scanning screen, and these two screens are combined to make up a full screen composed of a total of 525 scanning lines.
Therefore, in order to deliver a code on the screen once in every 1/60 sec, since the total number of scanning lines is 525, which is an odd number, there is a time difference between codes of one horizontal scanning time (63.492 .mu.sec) between the change from the first screen to the second screen and the change from the second screen to the first screen, which causes a serious problem that the picture and code cannot by accurately separated and recognized.